246 THE AMEEICAN MONTHLY [November, 



On a Bacterial Insect Disease. 



By S. a. FORBES, Ph. D., 



CHAMPAIGN, ILL, 



The student of human physiology often finds his subject brilliantly 

 illuminated by a knowledge of the far simpler physiological apparatus 

 and functions of the lower animals — of Arthropods especially — and it 

 has seemed to me quite possible that the pathology of these creatures 

 might sometimes similarly interest the student ot medical theory. As 

 a first venture in this direction, I submit a description of a bacterial dis- 

 ease of the notorious chinch bug {B/issits Iciicopteriis) , a hemipterous 

 insect about a sixth of an inch in length, the contagious diseases of 



As this disease is restricted to a single part of the digestive tract, a 

 which are now^ undergoing systematic investigation at my office, 

 brief description of this tract will be necessary; the more so, since it 

 has never yet been described, and because it presents some interesting 

 peculiarities. 



The alimentary canal of the chinch bug may be divided, in general 

 terms, into five regions of greatly different importance ; the oesopha- 

 gus, the gastric region, the coeca, the region of the Malpighian tubules 

 and their vestibule, and the rectum. The oesophagus is a very slender 

 short tube, about .i to .15 mm. long, opening abruptly into the broadly- 

 rounded anterior end of the first stomach. The gastric region is di- 

 vided into three quite distinct cavities, of which the first and largest 

 lies in the direction of the long axis of the body, the second at right 

 angles to it, and the third again in the direction of the first. The an- 

 terior division is slender-jDyriform or ovate, broadest behind the middle, 

 2 to 2.5 mm. long by about 8 mm. wide in its usual condition, with 

 a verv delicate outer wall, in which is a reticulum of muscular fibres 

 arranged in two sets, longitudinal and transverse. The latter are quite 

 regularly placed, .02 to .07 mm. apart, closest on the anterior part of 

 the stomach. These transverse filaments are about 4 ,a wide, branch 

 occasionally, and rarely anastomose. The longitudinal bands are less 

 regularly arranged, frequently branch dichotomously, and anastomose 

 variously, forming an open net-work with elongate meshes, the fibres 

 of which vary from 3 to 5 ,v. in diameter. 



The epithelium of this cavity is composed of a single layer of nearly 

 spherical cells (commonly granular and semi-opaque) of irregular size 

 and not closely crowded, varying in transverse diameter from .07 to 

 .15 mm., and in height from .06 to .09 mm. The inner surface is con- 

 sequently uneven, the cells projecting variously by broadly^rounded 

 ends. 



The first cavity connects immediately, b}' a narrow constriction, with 

 the second, smaller, obovate one, which is about .7 mm. long by .5 

 mm. in greatest breadth. This body is lined with very large pale cells 

 of irregular size, varying in diameter from .06 to .1 mm., and always 

 contains a large fluid mass varying in color from yellow to dark brown, 

 or even black, which is probably partly digested food. The epithelium 

 is rather thicker and more nearly columnar than that of the preceding 

 division. 



This second division connects at its broad end immediately by another 

 narrow passage, with a third cavity of similar shape, but smaller, about 



